JP2766528B2 - Electronic camera image data processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image processing device for an electronic camera.

[Conventional technology]

CCD instead of conventional silver halide photography camera
An electronic still camera using a solid-state imaging device such as the one described above has been developed. This electronic still camera converts a subject light into an electric signal, processes the converted electric signal appropriately, and records the processed signal on a recording medium.

FIG. 6 is a block diagram showing an example of an electronic still camera. An image of subject light 1 is formed on an image pickup device 52 by a lens 50 and a shutter 51, and is photoelectrically converted by a drive circuit 53 and then output as an analog image signal. The analog image signal is converted into a video signal such as a television signal by a signal processing circuit 54, converted into a digital video signal by an AD converter 55, and then stored in a buffer memory 56 capable of storing one screen of video signal. Stored temporarily. Buffer memory
The signal stored in 56 is compressed by an encoding circuit 57 and recorded in a memory pack 58.

[Problems to be solved by the invention]

When shooting with an electronic still camera, necessary adjustment operations include focus adjustment, exposure adjustment, and white balance adjustment. Conventionally, these adjustments require dedicated sensors,
It was not suitable for lowering the price of cameras. In addition, electronic still cameras need to be compatible in the market, and it is necessary to standardize the encoding method.

The present invention uses an international standardized system that is compatible in the market as an encoding system, and eliminates the need for sensors for various adjustments required when photographing a camera. The purpose is to provide.

[Means for solving the problem]

In a first aspect, an input image is divided into a plurality of blocks including N × N pixels, and a discrete cosine transform (DCT) is performed for each of the divided blocks. AC of any order of DCT coefficients of multiple blocks for luminance signal for focus adjustment
Output means for outputting a component.

In the second invention, an input image is divided into a plurality of blocks each including N × N pixels, and a discrete cosine transform (DCT) is performed for each of the divided blocks. Output means for outputting DC components of DCT coefficients of a plurality of blocks for a luminance signal for exposure adjustment.

Further, in the third aspect, the input image is divided into a plurality of blocks composed of N × N pixels, and a discrete cosine transform (DCT) is performed for each of the divided blocks. And output means for outputting DC components of a plurality of block DCT coefficients for the color difference signal for white balance.

(Operation)

In the case of focus adjustment of an electronic still camera, the position of the lens at which the spatial frequency of the CCD image obtained while moving the lens back and forth is highest can be considered as the focus position. Further, the exposure adjustment can be performed by adjusting the aperture so that the average value of the luminance signal can be found within a predetermined range if the average value can be obtained. Further, the white balance can be adjusted by photographing a white object and adjusting the offset so that the average value of the color difference signals RY and BY becomes zero. As described above, the focus, exposure, and white balance can be adjusted if the spatial frequency component and the average value are known.

In the present invention, N × N pixels are defined as one block, and
Dimensional Discrete Cosine Transform (DCT: Dsscrete Cosine Transf
When the DCT result is obtained, the DC component of the DCT result represents the average value of the area of N × N pixels, and the AC component shows a value very similar to the spatial frequency component. Therefore, focus, exposure,
Information necessary for each adjustment of the white balance is obtained.

〔Example〕

First, an international standardization method of a data compression method for a still image used in an electronic still camera will be described.

Figure 2 shows the “Baseline System” of the international standard system
It is a schematic diagram for explaining processing of. This system divides an input image into blocks of 8 × 8 pixels, and performs discrete cosine transform (DCT) for each block (processing S
1), quantization is performed by dividing the obtained DCT coefficient by each threshold of a quantization matrix composed of 8 × 8 thresholds (process S2). The difference between the DC component of the quantized DCT coefficient and the DC component quantized in the previous block is obtained, and the number of bits of the difference is subjected to Huffman coding. The AC component is subjected to zigzag scanning within the block and converted into a one-dimensional sequence, and then two-dimensional Huffman coding is performed on the number of consecutive zeros (ineffective coefficients) and the number of effective coefficient bits (processing S3 and S3).
S4).

At the time of the quantization in the process 2, a certain coefficient (scale factor) is set for each threshold value of the quantization matrix.
Is multiplied and quantization is performed. The coefficient adjusts the image quality and compression ratio of the compressed image. FIG. 3 shows the luminance signal Y.
FIG. 4 shows a quantization matrix for color difference signals I and Q, and FIG. 5 shows a table showing the order of zigzag scanning.

Note that the Huffman coding does not use the quantized coefficient value itself for both the DC component and the AC component, and the number of bits required to represent the value is input to the Huffman coding. Then, separately from the Huffman code, the value of the number of bits is added as additional information. For example, if the quantized coefficient is 2
(Decimal number), if expressed in binary number, "000… 01
However, the number of bits 2 required to represent the value is Huffman-encoded as a value representative of this value. Then, only two bits of data "10" are added as additional bits.

If the quantized coefficient is negative, data obtained by subtracting 1 from the additional bit is added. For example, when the quantized coefficient is -2 (decimal number), when expressed in a binary number (two's complement notation), it becomes "111... 110", and the lower two bits become additional bits. “01” obtained by subtracting “1” is added as an additional bit. By doing so, the additional bit starts with 1 when the quantized coefficient is positive, and starts with 0 when the quantized coefficient is negative, so that it is easy to distinguish between positive and negative.

FIG. 1 is a block diagram showing an embodiment of an image data processing apparatus in which the above-mentioned "Baseline System" data compression processing is hardened.

This device includes a DCT circuit 10 for performing discrete cosine transform on a block of 8 × 8 pixels, a pair of RAMs 11a and 11b for temporarily storing the converted DCT coefficients, a ROM 12 for storing an address conversion table for reading out while performing zigzag scanning, and a RAM.
11a, 11b and an address counter 13 for supplying address data to the ROM 12, ROMs 14 and 15 for storing respective threshold values of a quantization matrix of a luminance signal Y and color difference signals I and Q, and a bit shift circuit 16 for multiplying a scale factor. and
17, a divider 18 for performing quantization, a two-stage register 19 and a subtractor 20 for calculating a difference between DC components of quantized coefficients, a ROM 21 storing a Huffman table for DC components, and a quantized AC component. A comparator 22 for detecting the zero of the coefficient and a counter 23 for counting the continuity of the zero, when the coefficient of the quantized AC component is not zero, to hold the value and the number of consecutive zeros up to that point. , A ROM 25 storing a Huffman table for AC components, and a timing control circuit 26 for controlling the overall operation.

Further, as described above, the DC component of the DCT result in the DCT circuit 10 indicates the average value of the area of 8 × 8 pixels, and the AC component indicates a value very similar to the spatial frequency component. , Exposure, white balance and the like are obtained.

Therefore, in the present invention, the register 27 for setting the address for outputting the DCT coefficient in one block, the DCT circuit 10
The comparator 28 compares the address when the DCT coefficient output from the memory is input to the memory with the address set in the register 27, and determines the address where the DCT coefficient is input to the memory and the address set in the register 27. At the same time, a register 29 for holding the DCT coefficient is provided.

In this configuration, for example, the address setting register 27
If the address of the DC component for one block is set in the register 29, the DCT coefficients of the DC components of all blocks in one screen are stored in the register 29.
If the average value of these is obtained, a value necessary for exposure adjustment is obtained if the input of the DCT circuit 10 is a luminance signal, and a value necessary for white balance adjustment is obtained if the input is a color difference signal. Also, if the address of the AC component of any order is set in the address setting register 27, the DCT coefficient of the AC component is obtained, and the average value of all the blocks of the AC component of that order is obtained, and the average value becomes large. It is possible to adjust the focus by adjusting the position of the lens so as to be as follows.

〔The invention's effect〕

According to the present invention, dedicated sensors for focus, exposure, and white balance are not required, and the cost of the electronic still camera can be reduced. Further, since the international standardization method is adopted as the data compression method, it is suitable for an electronic still camera that needs to maintain compatibility.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image data processing device according to the present invention. FIG. 2 is a schematic diagram of a "Baseline System" of an international standardized system in a data compression system of an electronic still camera. FIG. 4 is a quantization matrix of a luminance signal, FIG. 4 is a quantization matrix of a color difference signal, FIG. 5 is a table of a zigzag scan, and FIG. 6 is a block diagram of an electronic still camera.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 5/225-5/238 H04N 9/04-9/09 H04N 9/64-9/73

Claims (3)

(57) [Claims] An input image is divided into a plurality of blocks each composed of N × N pixels, and a discrete cosine transform (DCT) is performed for each of the divided blocks. Output means for outputting an AC component of an arbitrary order of DCT coefficients of a plurality of blocks with respect to a luminance signal, the image data processing device for an electronic camera. 2. A conversion means for dividing an input image into a plurality of blocks each composed of N × N pixels, a discrete cosine transform (DCT) for each of the divided blocks, and an exposure adjustment based on an output of the conversion means. Output means for outputting DC components of a plurality of block DCT coefficients with respect to a luminance signal, for use in an image data processing device for an electronic camera. 3. A conversion means for dividing an input image into a plurality of blocks of N × N pixels, a discrete cosine transform (DCT) for each of the divided blocks, and a white balance based on an output of the conversion means. As for
Output means for outputting DC components of DCT coefficients of a plurality of blocks for a color difference signal, and an image data processing device for an electronic camera.